Semiconductor manufacturers are continually working to reduce time-to-market in an effort to improve serviceability while decreasing operating costs. Therefore, efforts have been made to develop and implement systems and methods such as continuous flow manufacturing, including operations management, which is also known as range management.
In a standard range management system, wafer processing operations are partitioned into a series of flows, where the products in each flow follow similar routings through the fabricator (fab). These flows are divided into ranges, where the expected cycle time of the work in progress (WIP) in each range is 24 hours. For example, a range may include the following operation sequence: lithography, metrology, overlay, and metrology CD.
In a range management system, each range has a daily takt rate (DTR) which is the ideal daily throughput rate for that range. Takt is a German word for “beat” and represents the pace at which product moves through the manufacturing process. In a standard range management scheme daily takt rates (DTRs) are static, changed infrequently, and set at a constant level across all ranges in a product flow.
Daily output targets for each range are set based on the DTR and also the amount of WIP in the range, and the amount of WIP in the next range. A standard range management matrix exists, that is used to determine the daily output targets. For example: the daily output target could be anywhere from zero, if the next range WIP is greater than 2.5× the DTR, to 1.25× the DTR if the next range WIP is lower than the DTR. When a range meets the target output for a day, the range is “stopped,” so that effort can be directed towards other lots, in ranges that still need to achieve the target output. In a standard range management system, targets are set once per day.
At the end of each day, the performance of each range is evaluated and compared with the target to identify problem areas. By operating the manufacturing line with this methodology, the WIP stays balanced and resources are evenly distributed.
The evaluation of targets only once a day, though, can cause problems due to the movement of WIP within the day. The WIP profile changes frequently, such that, to ensure WIP balance, some stopped ranges may need to be activated and conversely, ranges that are delivering WIP into over-WIP ranges may need to be stopped so that resources can be applied to move other WIP into under-WIP ranges.
In existing range management schemes, WIP is driven to conform to a static DTR profile. For example, even though a certain product may only be ramping up, the DTR is set at a flat rate across all ranges. The result is that the WIP is forced quickly through certain ranges, because they seem to be under-WIP, and stopped in other ranges to divert resources. This does not reflect the commits, and ignores the capacity of different parts of the line. In such situations, WIP is driven at varying rates, but is not produced at committed rates.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.